Time delay control



April 17,1951y F. G. WHITE 'mm DELAY connor.

2 Sheets-Sheet 1 Filed April 25, 1945 o 10a, L IO Ilja,

'wie

w N m; w m

E m 3A .R mm w April 17,1951 P. G. WHITE 2,549,149

TIME DELAY CONTROL lFiled April 25, 1945 `2 sheets-slim 2 INVENTOR. @ma im gy WM Umd/v, M

ATTO A/Ey Patented Apr. 17, 1951 TIME DELAY CONTROL Paul G. White, Cleveland, Ohio, assigner -to The -ElectricCnntroller & Manufacturing Company, Cleveland, .OhiQ, va corporation of Ohio Application April '25, 1945, Serial No. 590,218

14 Claims. (Cl. 17 5.-,320)

This invention relates to a control system for an electric translating device, -.the illustrative `ein amples hereinafter disclosed being improved control Vsystems for automatically short circuiting the resistance in a circuit of ,an electric motor during acceleration of the motor and for introducing a time delay ybetween lthe closing of ,successive starting switches, the extent ofthe .time delay intervals being dependent `upon therate of change ofthe energy in an electrical;energyaccumulation device such as acondenser.

Heretofore, in the control of .translatingidevces other than motors by timing circuits, itzhas'been proposed to .connect a condenser, an adjustable resistor, and the operatingwinding ofenelectro magnetic relay'in series with eachother across a source of substantial-ly constantunidirectional voltage, the electrical constants vof :the rcircuit being so proportioned that, uponinitial application of voltage to the circuit terminals,jthe initial impulse oi condenser charging current is gsuiiilcient -to cause pick-up or actuation of :the Ielay which temporarily yremains in 'its' actuated fior closed magnetic circuit .position until the condenser charging current decreasesto=the.dropout current value of the relay. A `series ,connected condenser, resistorand relay windingcircuitsuch v as just describedand in which all of the relay current passes through lthe timing condenseris not suitable foridetermining'the time delay-,intervals between the closing .of vsuccessive motor :acceleration switches because, when the -resistance of the circuit is made low enoughto permit the initial flow of charging current-tothe large enough to pick up the relay, the resistance is tooflowfto delay adequately vthe charging timefof'fthe4 condenser, and consequently the 'timingper-iod is Atco short for many purposes including that ,of motor starting control. This vdisadvantageis aggravated by low voltage conditions that often .occur on industrial power supply systems. The time rdelay period can obviously be increased by using-acondenser of larger capacity, but this expedient is generally not justified both because of :the .increased cost and because ;of '.theglarger space required. Another disadvantage .of the `simple series connected :timing circuit such as above .described is'that relatively large variations Pin the resistance of the resistor have but little effect on the time interval during which the relay isrin itsactuated position so Ythat other means vmust beresorted Yto in order to obtain the A,usual required adjustment of the duration of the timing period.

Bv taking advantare` .of :the phenomenon that substantially less current is required .120 rhQldza f relay in its actuated position than is required to actuate it, various modifications of the simple series connected timing circuit have heretofore ;nently suitable for use in controlling motor acceleration, each of the timingrelays Vrequires but a singleoperating winding, and connections are provided which conduct addtiional `current for .eiecting pick-up of the :relays Yand which 4also function to prolong the timing interval. More specifically .in accordance with this invention,

means such as Aa resistor is connected in parallel vwith the condenser and resistor portion of aseries connectedcondenser, resistor, and relay winding vtiming circuit thereby providing an additional path for current `flowing to the relay windingso that part of the current required :for picking up and holdingin Vtherelayrlows through the shuntingresistor and the remainder is suppliedthrough the-series connectedcondenser and resistor.Y The amount of `current owing through the shunting resistor when the condenser approaches its charged condition is less .than the drop-out current value of Ythe relay s o that therelay tem,-

jporarily remains in its lactuated position forka -time vinterval or until the sum ofthe condenser chargingcurrent and-the current flowing through thefshunting resistor .becomes less than the dropout current value ofthe relay. The'fcombination of such ahy-spass or shunting means with aseries connected condensenresistor, and relay winding timing circuit Vnot `only increases the maximum `duration of the timing interval obtainable with a given size of condenser, but also greatly increases -the range of adjustment vof the timing intervalrand vprovides a circuit useable for controlling-motor acceleration. By proper selection of;resistancevalues in the circuitofthe present invention, it is possible to obtain suiiicient time delay to control properly the acceleration of a motor driving a load of high inertia even though acondenser of:relatively low capacity is y,riscri-y ;;I.n one ,embodiment Qf :the invention ,herein disclosed one of the improved series connected condenser and relay winding timing circuits is provided for each motor starting switch which is to be operated at the expiration of a predetermined time interval. In another embodiment operation of a first motor starting switch which is time-controlled by one of the improved series connected condenser and relay winding timing circuits sets up circuits whereby the condenser used for timing the operation of the first switch also times the operation of a succeeding switch. During the second timing period of the condenser, the condenser discharges through a loop circuit including the operating Winding of a second relay, and connections including a resistor are provided to permit additional current to flow to the winding of a second relay directly from the source of supply during the timing period thereby causing the relay to be held in its actuated position for a longer period of time than if the condenser discharge current alone were used to hold the relay in its picked-up position.

An object of this invention is to provide an improved time .delay control system.

Another object is to provide a time delay control system which does not have the disadvantages and which has the advantages above set forth.

Another object is to provide an improved time delay control system in which an electromagnetic relay is temporarily held in its actuated or energized position by the charging current of a condenser connected in series with the operating winding of the relay.

A further object is to provide a time .delay control system in which a relay is temporarily held in its actuated position by the charging current of a condenser connected in series with a resistor and the relay winding and in which a circuit bypassing the condenser and resistor supplies part of the current for picking up and holding in the relay.

Another object is to provide an improved time delay control system in which the operating winding of an electromagnetic relay is initially supplied with current through a circuit bypassing a substantially discharged condenser connected in series with the winding.

Still another object is to provide a time delay control system in which an electromagnetic relay is temporarily held in its picked-up position by current iiowing to its operating winding through a parallel circuit having a resistor in one branch and a condenser and a resistor connected in series with each other in another branch.

A further object is to provide a time delay control system in which the operating winding of an electromagnetic switch is supplied through a parallel circuit having a gradually increasing current in one branch and a graduallyY decreasing current in another branch.

A still further object is to provide an improved timing circuit for a plurality of electromagnetic devices in which both the charging current and the discharging current of a condenser are used for controlling the devices.

An additional object is to provide an improved control system for an electric motor which includes means responsive to the charging current of a condenser for controlling the operation of electromagnetic switches.

Other objects include the provision of a plurality of cooperating time delay circuits each utilizing the charging time of a condenser, the

provision of a plurality of series connected con-v denser and relay winding timing circuits for controlling the acceleration of an electric motor, and the provision of an improved time delay control system in which both the charging and discharging intervals of a condenser are utilized.

A still further object is to provide a motor control system in which a relay, having normallyclosed contacts in series with the operating winding of a switch to be operated after a time delay, is operated to the open position of its contacts before a circuit to the switch can be completed and then is held in its operated position for a time interval measured by the charging time of a condenser.

Other objects and advantages will become apparent from "the following description wherein reference is made to the drawings, inwhich:

Fig. 1 is a circuit diagram illustrating the invention;

Fig. 2 is a circuit diagram of a modification;

Fig. 3 is a graph illustrating time-resistance characteristics of a prior art time delay circuit, and

Fig. 4 is a graph illustrating time-resistance characteristics obtainable with the time delay control circuit of Figs. 1 and 2.

Referring to Fig. l, a direct current motor I0 having an armature winding |0a and a series iield winding IIlb is arranged to be connected between a pair of supply conductors and l2 through series connected accelerating resistors I4 and |5 when normally open main circuit contacts IEa of an electromagnetic switch or contactor I6 are in their closed position. The switch I6 additionally has normally closed auxiliary contacts IED, normally open auxiliary contacts |60, and an operating winding I6w the energization of which is controlled by a pilot device or master switch shown as a push button I8 having normally open conas a push button I8 having normally open contacts |8a and normally closed contacts |819. The accelerating resistors I4 and l5 are arranged to be short circuited by normally open main circuit contacts Illa and 2Ba, respectively, or electromagnetic switches or contactors I9 and 20, respectively. The switch I9 is additionally provided with normally closed auxiliary contacts I9b and |9d, normally open auxiliary contacts |90, and an operating winding |910. The switch 2U has an operating winding 20w. The energization of the windings |9w and 20w is controlled by normally closed contacts 2|a and 22a, respectively, of electromagnetic relays 2| and 22, respectively. The relays 2| and 22 have operating windings 2|w and 221D, respectively, and are designed; preferably by having moving parts which are relatively much smaller than the moving parts of the switches I6, I9 and 20, so that they move to their operated position more quickly upon energization of their respective windings than do the switches. That is, when the winding of a switch and the winding of a relay are energized concurrently, the relay moves to its operated position before the switch. Any suitable type of relay may be used for the relays 2| and 22 so long as it has a drop-out current value which is less than its pick-up current value, but preferably the relays 2| and 22 are of the clapper type hav- 4ing either a xed drop-out current value or having means for adjusting the drop-out current value, it being understood that the representation of the switches and relays in the drawings is merely schematic.

For controlling time delayed drop-out of the lrelay 2|, a condenser 24 and an adjustable resister '25 are'conn'ected in 'series with .each other and with the windingiZ Izw betweenthe conductor I'21and a conductor I Ia 'whichzis electrically lconnected to the `conductor I I `when'.tl'iecontacits Aitc land/or I8a are closed. .The time delayed operation of the'relay 22 is controllediby connecting the condenser 24, the adjustable resistor l2.5, an adjustable resistor 216, and the windings 2 iw and .-22w in la closed loop circuit. In accordance with Ythis invention, resistors 28 and 29 of relatively high Aohmic value are provided in the energizing circuits of the relays 2| and22, respectively, for facilitating the adjustability and increasing the duration of the timing inter-vals in va manner to be described in the following description of .operation.

AWith the conductors I I vand 'I2 connected to a suitable source of direct current, closure .of the contacts IBa of `the push button I8 concurrently completes respective energizing circuits Vfor the windings Iw and 2 iw. The energizing circuit for r'the winding Iw extends through the contacts I'Bb, the winding Iw, anda conductor B'fto 'the conductor I2. The energizing circuit for the winding 2Iw has a plurality of parallel branc'hes' one of which extends vfrom rthe contacts Ia through aconductorl, the contacts Idd, theresistorf28, ay junction point 33, the winding 2Iw, and a conductor 32 to the conductor 1I 2. Another of the parallel branches extends from 'the -now energized conductor 3l `through vthe conductor I Ia, the contacts IBb, a branch point Stand the adjustable yresistor tothe junctionpoint 33. A third 'parallel branch ofthe energizing circuit for the winding r2I w is `from theconductor Iic :through a conductor '35, `the 'contacts 19h, 'a "con- .ductor `36, and the condenser 24 "to the branch point 313. The ohmic resistance of the resistor 28 and the maximum possible'resistance Vof the resistor 25 together with the resistance of ythewind- `ing 2Iw are so selected relative .to ther minimum expected voltage of the source that suicient current for operating the relay 2I flows through the branch point 33 to the winding '2'Iww`hile the contacts I 6b remain closed or whilethe 'condenser 24 is substantially discharged. Y

Openingof the :contacts '21a upon operation Aof the relay 2I `prevents immediate operation of the switch I9, the coil 'lliw of which is connectedbetween the conductors IIa .and I2 through the contacts 2id and a conductor 3l.' An energizing circuit for the winding "2210 'which isalso com pleted upon closure of the contacts I8a extends from the conductor I Ia .through the'conductoreli,r the .contacts ISb, the conductor 3e, the resistor 'i voperates to close its contacts Ita Vand 16o and to open its contacts |622. Closure of the contacts IBa connects the motor I iifto the'sourc'e ofpower in series with the resistors I4 and "I5, and Aclosure of the contactsI tccornpletesa circuit around the -contact Ita between the conductors 'II and vI Ia thus permitting the. contacts I'S'a to be opened. Opening of fthecon'tacts Iib permits a charging :current to flow through the condenser 2li and the relay .2| is thereafter .held in `its picked-up position 'by the .sum of the currents which flow through the branch circuit including the condenser '2li and the resistor 25 `and through the lbranch circuit including :the `resistor 28. The current iiowing through the .condenser 24 gradually Vdecreases as the .condenser accumulates a charge, and the current iiowing through theresistor 28 :gradually increases. The .resistor 28, however, has an ohmic value 'so vrelated to the voltage between the conductors .II .and .I2 .and lto the resistance .ofthe Winding 2Iw that insuf- 'ficient current can :flow therethrough to hold :the relay V2I 'in its actuated position. Consequently,

Ywhen the condenser 524 /becomescharged toa predetermined degree after a lapse of time determined `by-itscapacity, the resistance of its charging circuit, `and the applied voltage, the current 'flowing through the winding 2Iw becomes less than Vthe drop-outcurrent value of the relay 2i which thereupon drops out to close its contacts 21a.

Closure of the contacts 2m completes the energizing circuit previously traced for the winding Iiw .causing operation of the switch IQ. Movenient 'of the switch I9 'toits operated position causes 'closure of the contacts Id which short circuit thevresistor i4 thereby increasing the 'voltage applied `to the motor ill, and causes closureof the-'contacts lc which complete a holding circuit -forlth'e winding VI'iiw from the conductor -I-'ia through the contacts i 9c anda conductor 38 to the conductor 311. Thefcontacts Ish open .consequent upon operation of 'the `switch l 9 Vand interrupt the charging circuit for the `condenser `2t, and the contacts Idd also open to interrupt the last remaining circuit "between `the left-hand terminal of thecondenser 261 'and the conductor A closed loop circuit for the discharge of the condenser lZibeconies effective upon operation of theswitch y'I9 and extends from the right-hand terminal of the condenser-2,4 through the resistor ft, the winding 222e., the-conductors i2 and 32, the winding 2Iw, and the resistor 25 to the left hand terminal of the condenser. The discharge current of the condenser 2:3 together with the currentowing through the resistor v2Q holds the `relay 2-2 in its picked-up position fora period of time dependent upon the amount of charge on the condenser 24 and the resistance of the discharge loop. The ohmic value of the resistor 29 fis so chosen that during the discharge period of :thecondenser 21B acurrent slightly less than the drop-out current value of the relay 22 iiows Ythrough the resistor 29 to the winding 22er. When vthe condenser 24 has discharged to a predetermined Llow value, the sum ofthe currents owing through the condenser 2d and the resistor 28 becomesless than the'drop-out .current value of the resistor I5 to-connect the 'motor Iii directly across the Vsource of power. vThe resistor 26 maybe omitted, if desired, providedthe winding 22u: has suicient resistance to limit the current flowing tothe winding through Using a condenser vhaving a capacity of 40 microfarads, a total time delay period of fourteen seconds was obtained between the instant of pickup of the relay 2| and the instant of drop-out of the relay 22 when the supply potential was 230 volts, the resistors 28 and 29 each had a resistance of 100,000 ohms, the windings 2 |w and 221D each had a resistance of 8400 ohms, the resistor 25 was adjusted to have a resistance of 25,000 ohms, and the resistor 26 was not used. The foregoing values are given by way of addtional explanation only and are not to be considered as limiting Values in any sense.

In Fig. 3 which illustrates the operation of a prior art timing circuit comprising a condenser, a resistor, and a relay winding connected in series and in which all of the relay current flows through the condenser, the time during which the relay is held in its operated position by the charging current of the condenser is plotted against adjusted values of the series resistor. A curve 4| is the time-resistance characteristic of such a circuit in which the condenser has a given capacity C, and curves 42 and 43 are time-resistance characteristics of similar circuits having a condenser with a capacity of twice C and four times C, respectively. It is to be noted that as the capacity of the condenser is increased, time delay periods of increased duration result, and that by increasing the ohmic value R of the resistor, relatively small increases in the time delay period are obtained. In order to prolong the flow of condenser charging current, it is necessary to increase as much as possible the ohmic value of the series resistor, but if, as in the prior art circuit being considered, the initial impulse of condenser charging current alone is used to pick up the relay, there is a limit beyond which it is impossible to increase the resistance of the circuit. This limiting value of the resistor for a particular value of supply voltage and for a particular relay is represented by a curve 45 in Fig. 3, it being obvious that if the supply voltage has any lesser value, the limiting resistance curve 45 moves to the left.

Referring now to Fig. 4, which shows timeresistance characteristics of the timing circuit including the relay 2| as connected in Fig. l, the units of both the time scale and the resistance scale are ten times as large as the corresponding scales of Fig. 3, hence the indication of the ordinate point IDT and the abscissa point IDR. A similar relay was used to obtain the data for Figs. 3 and 4, and in Fig- 4 curves 46, 41 and 48 are plotted for the same values of capacity as the curves 4|, 42, and 43, respectively, of Fig. 3. Since in the circuit of Fig. l all of the current necessary for picking up the relay 2| does not ow through the resistor 25, the resistor 25 may have a larger value than otherwise would be possible.

In the embodiment of Fig. 2, a timing condenser is provided for each resistance shunting acceleration switch and the charging time only of the condensers is utilized. The relays 2| and 22 of Fig. 2 may be the same as the relays 2| and 22 of Fig. 1. As distinguished from Fig. 1, in Fig. 2 the switch |6 has normally open contacts |6a and |6b only, the contact |911 of the switch i9 is normally open instead of normally closed, and the switch 20 is provided with a normally closed auxiliary contact 20h and a normally open auxiliary contact 20c. A condenser 60 and an adjustable resistor 6| of relatively low ohmic value are connected in series with the winding Zlw, and a condenser 62 and an adjustable resistor 64 of relatively low ohmic value are connected in series with the winding 22w. For supplying part of the current for picking-up and holding-in the relay 2l, a resistor 65 of relatively high ohmic value is connected in parallel with the condenser 60 and the resistor 6|, and similarly, for supplying part of the current for picking-up and holding-in the relay 22, a resistor 66 of relatively high ohmic value is connected in parallel with the condenser 62 and the resistor 64. Other details of the motor starter of Fig. 2 will become apparent from the following description of operation:

With unidirectional voltage available at the supply conductors and l2, closure of the contacts |8a concurrently completes energizing circuits for the windings |6w and 2|w. The energizing circuit for the winding |6w includes the stop contacts |8b and the conductor 30. The energizing circuit for the winding 2|w includes the normally closed contacts |9b and the Aparallel circuit having the resistor 65 in one branch and the series connected condenser 60 and resistor 6| in the other branch. The resistances of the resistors 6| and 65 and of the winding 2|w are so related to each other and to the voltage across the conductors and |2 that, if the condenser 60 is substantially discharged, the combined current flowing through the parallel connected resistors 6| and 65 is sucient to actuate the relay 2| thereby causing opening of the contacts 2Ia. As explained in connection with Fig. 1, the contacts 2|a open before current owing through the winding ISw can cause operation of the switch I9. Operation of the switch |6 in response to the energization of its winding |6w results in closure of the contacts |6a connecting the motor I0 across the conductors and |2 in series with the resistors I4 and l5.

Charging current flowing through the condenser 60 and the resistor 6| combined with that flowing through the resistor 65 holds the relay 2| in its actuated position until the condenser 60 is substantially charged, When the condenser 60 reaches a predetermined charged condition, the relay 2| drops out and closes its contacts 2 la. completing the energizing circuit for the winding |8w of the switch I9. Operation of the switch I9 causes closure of the contacts |9a thereby increasing the voltage applied to the motor |0, causes closure of the contacts |9d to complete a low resistance discharge circuit forthe condenser 60 through a small portion of the resistor 6|, and causes opening of the contacts |9b to prevent re-actuation of the relay 2|.

Operation of the switch I9 also causes closure of the contacts to connect the conductor ||a to a conductor ||b and thus completes an energizing circuit for the winding 22w which circuit includes the contacts 20h and a parallel circuit having a branch including the series connected condenser 62 and the resistor 64 and a branch including the resistor 66. If the condenser 62 is substantially discharged, the combined current z' which flows initially through the branch circuits is suicient to cause actuation of the relay 22 thereby opening the contacts 22a to prevent operative energization of the winding 20w which is connected across the conductors ||b and I2 in series with the contacts 22a. During the accumulation of a charge on the condenser 62, the current flowing through the condenser 62 and the resistor 64 decreases to a value less than the drop-out current value of the relay 22, but the relay 22 remains in its actuated position for a furtherv timey interval. due to the additional` cur;- rent flowing through the resistor 66. .Eventually the condenser 62 becomesy charged to such a value that theI sum of the, currents flowing in the two parallel branch circuits is less than the drop,- out current value of the relay 22 which thereupon returns to its normal position in which thev con tacts 22avarel closed.

Y Reclosure ofthe contacts 22a, causes energization of the winding Ztw of the switch 20 which responds to close the contacts waandtic open the contacts 2Gb'. Closure of the contacts 20a short circuits the remaining resistor l5 so vas to connect the motor I directly across the con ductors I l and l2, and closure. of the contacts 20c completes an obvious discharge circuit of low resistance lor the condenser 62d througha portion of the resistor 6d, Opening ofthe contacts 20o prevents reactuation of the. relay 2K2.

The rmotor I0 is thus gradually -accelerated as a consequence ofV the time delay intervals provided by the charging time of: the condensers 56 and 62. Opening or the contacts lb at any time causes disconnection of the motor i@ from the source of supply and dropout of the switches IE, I9 and 20 as well as the relays 2| and 22. The low resistance condenser discharge circuits that are completed upon drop-out of the switches I9 and 20, respectively, permit proper time-delayed re-acceleration of the motor id should the contacts Ilia be closed immediately after the contacts liloy have been operated.

I claim:

l. In a time delay control the combination with a condenser, an electromagnetic relay having an operating winding and operative to pick up and to drop out at predetermined current values respectively in said, winding, and connections for connecting said condenserand said winding in series with each other across ak source of unidirectional voltage, of a by-pass circuit connected in parallel with said condenser and operative during the charging period of said condenser to provide an additional path for ycurrent flowing to said winding, a resistor in said by-pass circuit, and the` resistance of said resistor and said relay winding being so related to the voltage of said source that a combined current greater than the drop-out current value of the relay iiows through said resistor and said condenser to said winding after the charging current of said condenser has decreased below said drop-out current value and oeingl further so related to the voltage of the source that a current having a valueslightly lless than the drop-out current value of 'said relay iiows through said Icy-pass circuit to said winding when said condenser approaches a charged condition.

2. A' time delay control comprising a condenser, a rst resistor, an electromagnetic relay having an operating winding, connections for connecting said condenser, said rst resistor, and said windingV in series across asourceof unidirec# tional voltage, said rst resistor and said winding having a combined ohmic resistance so related to the voltage of said source that insuflicient current flows through said rst resistor and said condenser to actuate said relay, a by-pass circuit connected in series with said winding and in parallel with said condenser and said rst resistor and a second resistor in said by-pass circuit, the ohrnic resistance of said by-pass circuitbeing so related to the voltage of said source that the sum of the current flowing through said by-pass circuit and through said condenser andsaid rst and; to,

10 resistor when said condenser is substantially discharged, is suicient to actuate said relay.

3. A time; delay control Comprising a` condensen, a resistor, an electromagnetic relay having an operating Winding, connections for con,` necting said condenser, said resistor, and said winding in series across; a source of: unidirectional 1 voltage, saidresistor and said windingY having a combined ohmic resistance so related to the vol-.tage ofsaid., source that; insufcient current flows;v through saidA resistor andV said condenser to actuate said relay when said condenser is uncharged, and means completing a circuit. in parallel withsaid condenser and said resistor and iii-series with said winding, the combined resistance ofxsaidyparallel circuit and said winding bei-ng Sorelated to the voltage of; said source that the sum of the current owing through said parallel; circuit and the current owing through said condenserand resistor when said condenser is suns-tantiallyl discharged is sufcient to actuate Said relay,4 and the resistance of said parallel circuity and said windingfbeing further so related to the Voltage of said source that the current flowing through said parallel circuit and through said condenser and resistor when said condenser is substantialy charged is insuiicent to hold said relay in its actuated position.

e, A. timing control system, conff..prisingl an elec-4 tromagnetic device which has an operating winding andi which, becomes operatively deenerg-ized upon decrease of current in said winding below a predetermined value, a supply circuit for s aid winding including a :first resistor anda condenser connected in series with each other and with said winding and av second resistor connected in parallel with sai-d first resistor and said condenser and in seriesv withy said winding, means operable to connect said circuit for energization from a source of unidirectional voltage, energization of; said circuit causing a charging current to now through said condenser and a current to now through said second resistor, thek sum of said currents being suiiicient to cause operative energization of said electromagnetic device, and said second resistor and said electromagnetic deviceA having constants so related to the voltage of said sourcer that saidr electromagnetic device remains operatively energized for an appreciable timel interval after the current flowing through saidv condenser during the charging period of said condenser decreases below said predeterminedy value andthen becomes operatively deenergized. l

5. A timing contr-ol system comprising an electromagnetic device which has an operating winding, a supply circuit for said winding including a first resistor and a condenser connected in series with eachother and with said winding and .asecond resistor connected in series with said Winding and in parallelwith said rst resistor and said condenser, means operable to connect, said circuit for energization from a source of unidirectional voltage, energization of said circuit causing a charging current to How through said condenser which is insuilicient to cause actuation of said electromagnetic device and also causing a current to flow through said second resistor, the sum of said currents being sufficient to cause actuation of said electromagnetic device, and said second resistor and said electromagnetic device having constants so related to the voltage of. said source that said electromagnetic device becomes. operatively deenergized during the charging period of said condenser.

6. A timing control system comprising an electromagnetic device having a winding, a supply circuit for said winding including a nrst resistor and a condenser connected in series Awith each other land with said winding, a second resistor connected in series with said winding and in parallel with said iirst resistor and said cond`enser,'means operable to energize said circuit by connecting said circuit across a source of unidirectional voltage, the electrical constants of said circuit and of said electromagnetic device being so related to the voltage of said source that upon operation of said means with said condenser substantially discharged neither said first resistor and said condenser nor said second resistor conducts sufficient current to operatively energize said electromagnetic device but said electrical constants being so related to the voltage of said source that the sum of said currents is suilicient to operatively energize said electromagnetic device, and said second resistor and said electromagnetic device having constants so related to the voltage of said source that said electromagnetic device becomes operatively deener'gized during the charging period of said condenser.

7. In a time delay control the combination with a condenser, a timing resistor, an electromagnetic relay having an operating winding, and connections for connecting said condenser, sad'resistor, and said winding in series with each other across a source of unidirectional voltage, of a resistive by-pass circuit permanently connected in' parallel with said condenser to provide an additional path for current flowing to said winding and having a resistance such that the current in said additional path is less than the drop-out current value of said relay and operatively increases the iiux produced by the Winding.

8. In a time delay control the combination with a condenser, an electromagnetic relay havingan operating winding, and connections for connecting said condenser and said Winding in series with each other across a source of unidirectional voltage, of a by-pass circuit connected in parallel with said condenser and operative during the charging period of said condenser to provide an additional path for current ilowing to said winding, the sum of the currents flowing to said winding through said condenser and said by-pass circuit being greater than the pick-up current value of said relay, and a resistor in said by-pass circuit, the resistance of said resistor and vof said relay winding being so related to the voltage of said source that the current flowing through said by-pass circuit operatively increases the flux produced by said winding while remaining below the drop-out current value of said relay.

9. A timing control system comprising a condenser, a resistor, an electromagnetic relay having an operating winding, connections for completing a charging circuit for said condenser through said resistor and said winding in series from a source of unidirectional voltage, a by-pass circuit including a resistance means and connected in parallel with said condenser and resistor and in series with said winding and operative to supply to said winding a current sufficient, when combined with current iiowing in said charging circuit, to cause pick up of said relay by the combined current and operative, when said condenser approaches a charged condition, to limit the current supplied to said winding sufficiently to cause drop out of said relay, and means connected in said by-pass circuit and operative in response to drop-out of said relay for interrupting said by-pass circuit.

10. A timing control system in accordance with claim 4 characterized in that a second electroresponsive means has an operating winding connected in parallel with said condenser and which becomes operatively energized upon connection of said supply circuit for energization, switch means are connected in said supply circuit and are operable upon said operative deenergization of said nrst electromagnetic device to disconnect said supply circuit from said source while maintaining said operating winding of said second device connected in parallel with said capacitor, whereby operation of said switch means permits said condenser to discharge through said parallel connected Winding, there are a third resistor and a holding circuit connecting said third resistor and said second winding across said source, the electrical constants of said condenser, said second device, and said third resistor are so related to the voltage of said source that the winding of said second device remains operatively energized after said supply circuit is disconnected and for a predetermined time after the discharge current of said condenser decreases below the drop-out current value of said second device.

11. A timing control system comprising an electromagnetic device having a Winding and operative to move to a picked-up position when the current in said winding is above a predetermined pick-up value and to move to a droppedout position when the current in said Winding becomes less than a predetermined drop-out value less than said pick-up value, a supply circuit for said winding including a charging resistor and a condenser connected in series with each other and with said winding and a by-pass resistor connected in series with said Winding and in parallel with said charging resistor and said condenser, means operable to energize said circuit by connecting said circuit across a source of unidirectional voltage, the electrical constants of said circuit and of said electromagnetic device being so related to the voltage of the source that upon operation of said means with said condenser substantially discharged neither the charging current which flows through said charging resistor and said condenser nor the by-pass current which flows through said by-pass resistor is above said pick-up value but said electrical constants being so related to the voltage of the source that the sum of said charging and by-pass currents is above said pick-up value, and said electrical constants being further related to the voltage of the source that the charging current is above said drop-out value when said condenser is uncharged, said by-pass current is at all times less than said drop-out value, and said charging current decreases below said drop-out value during the charging period of said condenser while the sum of said charging and said by-passcurrents remains above said drop-out value.

12. A time delay control comprising a condenser, connections for connecting said condenser across a source of unidirectional voltage, a switch in said connections closeable to permit charging of said condenser from said source, an electromagnetic device having an operating winding and capable of becoming operatively deenergized upon decrease of current in said winding below a predetermined drop-out value, said winding being connected in parallel with said condenser and in series with said switch, a resistor connected in series with said winding and in parallel with said switch, the electrical constants of said device being so related to the voltage or said source that said device einains in operative position so long as said switch is closed and said condenser is charged, the electrical constants of said condenser, said resistor, and said device being so rc lated to each other that upon opening of said switch the current flowing to said winding through said resistor is and remains less than the drop out current value oi said device whe 1eas the sum of the current flowing to said winding Yirorn said condenser and the current owing to said winding through said resistor remains above the drop out current value oi said device ior a tirne interval.

13, A time delay control comprising a resistance means, a switch operable when closed to connect one end of said resistance means to one side ci a source oi direct current, a condenser, means connecting said condenser between said one end of said resistance means and the other side of said source of current, resistor connected between said one side oi said source and the other end of said resistance means, an electromagnetic device having an operating winding connected between said other side of said source and said other end of said resistance means, and the electrical constants of said resistance rneans, said condenser, said resistor, and said device being so related to each other and to the voltage or said source that upon closure of said switch said de vice moves to an operated position and said condenser beccrnes charged and that upon opening of said switch the sum of the current owing to said winding from said condenser and the current nowing to the winding through said resistor is sufcient to hold said device in operated position whereas the current ilowing to said winding' through said resistor is insufficient of itself to hold said device in operated position.

14. A timing control system comprising an electro-magnetic relay having a winding, a supply circuit for said winding including a iirst resistor and a condenser connected in series with each other and with said winding and a secondresistor connected in series with said winding and in parallel with said rst resistor and said condenser, a

pair of electroresponsive devices having respective energizing circuits, means operable tc connect concurrently said supply circuit and said energizing circuits in parallel with each other across a source or unidirectional voltage, the electrical constants oi said supply circuit and of said relay being so related to the voltage of said source that upon operation of said means when said condenser is substantially discharged neither said first resistor and said condenser nor said second resistor conducts suiiicient current to operatively energize said relay but said electrical constants being so related to the voltage of said source that the sum oi said currents is sufficient to operatively energize said relay, said relay having normally closed contacts in one of said energizing circuits operative to open, upon said concurrent connection oi said circuits across the source, and thereby interrupt said one energizing circuit while said other energizing circuit is maintained, and said second resistor and said electromagnetic device having constants so related to the voltage of said source that said relay becomes operatively deenergized during the charging period ci said condenser and thereby recloses said contacts, completing said one energizing circuit.

PAUL G. YWEIITE.

REFERENCES CITED foilowing references are of record in the le of this patent:

UNETEE STATES IPA'IENTS Number Nance Date 931,919 Dickinson Jan. 17, 1911 1,555,393 Thompson Oct. 6, 1925 1,759,255 Hudd May 13, 1939 1,939,609 Minller Dec. 12, 1933 2,089,273 Holmes May l1, 1937 2,187,637 Marbury Dec. 5, 1939 2,279,849 Warrington Apr. 1li, 1942 2,317,888 Cypser Apr. 27, 1948 2,339,750 Bartholy Jan. 25, 1944 2,375,229 Klemperer May 8, 194:5

FOREEGN PATENTS Number Country Date 56,246 Norway Mar. 2, 1936 

